To assess events of freedom from ipsilateral breast recurrence occurrences in patients receiving partial breast proton radiation therapy limited to the region of the tumor. [ Time Frame: At 3 years ] [ Designated as safety issue: No ]

Freedom from failure (FFF): The events for FFF will be the first ipsilateral breast cancer recurrence. It is expected that less than 3% of patients will experience an ipsilateral breast cancer recurrence (FFF ≥ 97%). A recurrence rate of ≥ 15% (FFF ≤ 85%) is considered unacceptable. Therefore, the null hypothesis is the FFF of ipsilateral breast cancer recurrence is 85% or lower and the alternative hypothesis is that FFF of ipsilateral breast cancer is 97% or higher.

Assess number and severity of acute and long-term toxicity of partial breast irradiation using proton therapy for the treatment of early stage breast cancer. [ Time Frame: On average every 6 months for life ] [ Designated as safety issue: Yes ]

To assess relationship between breast size and partial breast dosimetry. [ Time Frame: Average every 6 months for 3 years ] [ Designated as safety issue: No ]

The purpose of this research study is to compare the effects (good and bad) on women and their cancer using proton radiation therapy.

This study is being done to see if proton radiation therapy will prove to be beneficial for women with early stage breast cancer. A clinical study is necessary to compare the results (good or bad) of proton radiation therapy.

Detailed Description

Current standard of care for early stage breast cancer is mastectomy or breast conserving therapy with whole breast irradiation following lumpectomy. However, studies of breast cancer recurrence have demonstrated the majority of tumors to recur in or adjacent to the original tumor site. The question has thus been raised as to whether radiation to the whole breast is necessary or justified. Limiting radiation to the area of the original tumor may reduce acute and long-term skin and organ toxicities while making radiation therapy more convenient and less expensive. Several clinical trials are underway comparing partial breast irradiation (PBI) to whole breast irradiation. Numerous centers are offering partial breast irradiation outside of clinical trials as well, despite the lack of long-term safety and efficacy data on PBI.

Available PBI methods include brachytherapy, in which catheters or balloons are surgically inserted to deliver radiation therapy to the lumpectomy cavity, and conventional external beam radiation therapy, or EBRT. External beam photon therapy is attractive for its non-invasive nature and ability to deliver a more homogenous dose distribution compared to brachytherapy, however it also delivers a greater radiation dose to surrounding normal breast tissue.Proton therapy has the capacity to provide the same advantages as photon EBRT while minimizing dose to normal surrounding tissue. Clinical data on PBI with protons is minimal, however, leaving many questions unanswered. The impetus behind this protocol is to address these gaps by further investigating the feasibility, safety, and efficacy of proton therapy for partial breast irradiation.

One of the following criteria must be met: (a) Tumors that are microscopically multifocal must be 3.0 cm or less and encompassed within a single scar (b) Patient does not have microscopically multifocal tumor.

In the presence of extensive intraductal component (EIC) the entire pathologic tumor size (including both the intraductal and invasive component) are 3.0 cm or less.